Pump and double-acting motor hydraulic system, including control valve mechanism



Oct. 13, 1953 J c. NAYLOR ET AL 2,654,998

PUMP AND DOUBLE-ACTING MOTOR HYDRAULIC SYSTEM, INCLUDING CONTROL VALVE MECHANISM Filed July 12, 1952 doflHuA CHALLINER NAyL K w JOHN NELSON FlELDHOUSE 7 Sheets-Sheet 1 Oct. 13, 1953 J. c. NAYLOR ET AL 2,654,998

PUMP AND DOUBLE-ACTING MOTOR HYDRAULIC SYSTEM, INCLUDING CONTROL VALVE MECHANISM Filed July 12, 1952 7 Sheets-Sheet 2 40s 56 49 51-- s5 55 47 39 50 57a 37 v a a a 49!? J .5. 3O 55 9 WE MW 202 3 7g. INVENT KS JOSHUA LHALLIIN'E'R NAy oR w J N NELSM FIELD HousE AGENTS.

Oct. 13, 1953 J. c. NAYLOR ET AL ,998

PUMP AND DOUBLE-ACTING MOTOR HYDRAULIC SYSTEM, INCLUDING CONTROL VALVE MECHANISM Filed July 12, 1952 7 Sheets-Sheet 3 lNvEN-rm JOSHUA CHALUNE'K NAYLO'R AN) JoHN NELSDN FIELD HOUSE A ENT-5'.

2,654,998 SYSTEM, INCLUDING Oct. 13, 1953 J. C. NAYLOR ET AL CTING MOTOR HYDRAULIC CONTROL VALVE MECHANISM PUMP AND DOUBLE-A 7 Sheets-Sheet 4 Filed July 12, 1952 uau wall/110% JOSHUA CHALLINER MAyLDR AN) dorm NELSON FIELDHOUSE.

MHZ].

g AGENTS.

2,654,998 UDING Oct. 13, 1953 J. c. NAYLOR ET AL PUMP AND DOUBLE-ACTING MOTOR HYDRAULIC SYSTEM, INCL CONTROL VALVE MECHANISM 7 Sheets-Sheet 5 Filed July 12, 1952 INVENTIJRS ouSE M Mrs \45 452 j sHuA CHHLLINER uAyLoR AN) JOHN BY E DH Oct. 13, 1953 c NAYLOR ET AL 2,654,998

PUMP AND DOUBLE-ACTING MOTOR HYDRAULIC SYSTEM, INCLUDING CONTROL VALVE MECHANISM 7 Sheets-Sheet 6 Filed July 12, 1952 INVENTORS JOSHUA CHALLWE'R, NAyLoR AND J H NELSON Fl ELDHOUSE f.

AQEN S 2 54,998 CLUDING Oct. 13, 1953 J. c. NAYLOR ET AL PUMP AND DOUBLE-ACTING MOTOR HYDRAULIC SYSTEM, IN

CONTROL VALVE MECHANISM Filed July 12, 1952 7 Sheets-Sheet 7 INVE NTDKS Lwrmusa r A. AGENTS gnu/ cHALLmER NAyLoR AN) JOHN NELSoN 2E Patented Oct. 13, 1953 UNITED STATES PATENT OFFICE PUMP AND DOUBLE-ACTING MOTOR HY DRAULIC SYSTEM,

INCLUDING CON- TROL VALVE MECHANISM ish company Application July 12, 1952, Serial No. 298,646 In Great Britain August 24, 1951 Claims.

1 This invention relates to a hydraulic control system for a bulldozer and the like in which there is provided hydraulic fluid pressure actuated driver means, manually controlled valve means and fluid pressure generating means, to establish selectively a combination of connections between the fluid pressure actuated driver means, the fluid pressure generating means and/ or an oil reservoir as required, for raising, maintaining raised, lowering or floating a load such as, e. g. the blade of a bulldozer.

According to the present invention the hydraulic control system is characterised by the provision of means responding to the fluid pressure conditions in various parts of the system obtaining as the result of the various settings of the valve means, which, accordingto the setting of the valve means serve to automatically connect the driver to or isolates it from discharge of hydraulic fluid and so responds to fluid pressure in the pump circuit during actuation of the driver means as to maintain the discharge from the driver means at the correct proportionate rate to the rate of pressure feed from the pump to maintain a completely full hydraulic system.

Further in accordance with the present invention means for controlling the raising, lowering, maintaining raised and floating conditions of a bulldozer blade or other load to be controlled hydraulically under similar conditions, comprises a hydraulically actuated driver connected to the load to raise and lower the load, .a pump to feed hydraulic pressure fluid to said driver, a discharge outlet from the driver, a main valve controllable manually to load raise, lower, hold and float settings for controlling the connection of the pump to said driver, means to close said discharge outlet yieldingly opposing but actuated by the load raising and lowering driveroperative hydraulic pressure from the pump to connect said driver to said discharge outlet when the said main valve is actuated to the raise and lower settings and thereupon to connect the pump operatively to the driver so that the discharge from said driver must be proportional to the rate of pressure feed from the pump to said driver.

The hydraulic circuit of the present invention can be regarded as incorporating a valve of the spool type set in selected position by a manually controlled lever or other suitable remote control means to control the connection of a pump feeding the hydraulic fluid under pressure to the jack or jacks or equivalent means for raising and lowering the blade or load and also for circulating the oil idly while the loaded jack or the like is held in selected position, the circuit including also a counter-balance valve normally held in the closed position to retain oil in the appropriate part of the hydraulic circuit without pump pressure so as to block such part of the circuit, cushioning means, e. g. a spring, maintaining the valve in this normal position, the influence of this cushioning means bein overcome by pressure derived from the pump discharge during the operation of raising or lowering the blade or other load before discharge from the jack cylinder or cylinders or the equivalent thereof can take place, so that the discharge from the said cylinder or cylinders must be proportional to the rate of pressure feed from the pump to the jack cylinder or cylinders, and also there being provided between the aforesaid counterbalance valve and a branch from the pressure line from the pump to the jack cylinder or cylinders a counter-balance control valve which adapts itself automatically to the appropriate position in conformity with the line being served by the pump, whereby the pressure in the pump circuit cannot be applied to the first mentioned counter-balance valve to open the discharge from the jack cylinder or cylinders until the second mentioned counter-balance control valve is opened.

In order that the invention may be clearly understood and readily carried into effect drawings are appended hereto illustrating an embodiment thereof, and wherein,

Figures 1 to 7 are diagrammatic views all showing the same circuit appropriate to the valve and showing respectively the relative positions of the parts of the valve mechanism at the following stages of the position and actuation of the bulldozer: hold, raise, lower, float down, float up, approaching lower and approaching raise.

Figure 8 is a side elevation of the valve gear and oil reservoir with a cooler, the reservoir and cooler being in section.

Figure 9 is a front elevation view of Figure 8 with a front section of the reservoir removed to show the valve mechanism.

Figure 10 is a sectional front elevation of the main valve.

Figure 11 is a section on the line XI-XI oi. Figure 10.

Figure 12 is a section on the line X[IXII of Figure 10.

Figure 13 is a section on the line XIII-XIII of-Figure 10.

Figure 14 is a section on the line XIV-XIV of Figure 10, and

Figure 15 is a sectional front elevation showing detailsof an-overload valve.

Referring to the drawings, the pumping means and valve gear for supplying fluid controlling the hydraulic fluid pressure required to actuate a jack or pair of jacks connected to the blade of a bulldozer, are accommodated within an floil' reservoir l sealed against ingress of foreign matter, the hydraulic circuit being fed from any suitable form of such pumping means which preferably is, as shown, a radial blade type p mp 2 having a discharge conduit 3 to the main control valve 4 which is of the manually operated push-pull spool type having a spool 5 .slidably supported within a bore 6 of a valve housing 1 and prolonged beyond this bore to form a stem 8 about which is disposed a coiled compression :spring 9 operating against opposed abutments l and II :on the .stem to maintain the valvein the normal position .so that .it :can be loaded [in either :direcition :of operation .of the valve spool from the normal-position and thereby assisting the return of the valve spool to the normal position. The :spool is operated by za-crank .Bl (see .Figure 9) lomarshaftfl journalled in bearings with suitable m1 seals passed through the sides of the reservoir l and carrying .at one :exposed end a crank -6-3 (see Figure 8) by which the shaft is connected to :a'eontrol handle. The crank 6=l is connected to the spoolfi by a pair of links -64 and the spool :is inormally .retained in the hold position as shown in Figure 10 by thespool centering spring 3. rzacceomplished by the operator moving the valve spool in the appropriate direction against the action -of the centering spring which returns the spool when the control handle is released. To ,obtain thecondition knownas float which follows lower :the operator moves the valve spool ltur-ther against the additional resistance of spring .6 :acting :against the .detent lever 641) through roller -63 carried in forkedllever 65 pivoted :at -.66. The roller engages the .detent and holds the valve spool in this position until forcibly released,

A jack ,is indicated diagrammatically by the reference numeral [2, the load due to the Weight lof the bulldozer blade .(not shown) being in the .directiomof thearrow W. Discharge of oil from .the jack ,cylinder 13 due to the displacement of the piston I4 is finally via ,a counter-balance walve 15 which normally is spring loaded to .the position cuts .off the escape of oil .to the reservoir .50 that the oil in the appropriate .part of the circuit is -Jcilocked under substantially .no ,pressure. This counter-balance valve 15 is (embodied in the main valve housing "as shown in Figure 13. .In the diagrammatic Figures '1 to '7 this valve I5 is shown, purely for simplifying the diagrams, the reverse way to the actual arrangement shown in Figure .13.

'The counter-balance valve [5 can -be "spring ,loaded to the ,position which cuts 'off "the return .of the .oil to the reservoir -by constructing the valve as of the substantially balanced sliding ,piston type, i. e. with a valve stem 1'6 having a recessed head IT at one end in whichis engaged a -coiled compression spring [8 also engaged :in a fixed cup or abutment member l9 coaxial with the valve, the said recessed head l-l forming a part which closes a port in the housing of the nounter balance valve l5 through which the oil escapes via outlet 20a to the reservoir. The

The operations of flower and raise are valve stem at its end removed from the said recessed head is formed with another cylindrical recessed head 2| which is exposed at its outer end to fluid pressure fromza-conduit 22,, so that the free escape of oil to the reservoir is controlled by the fluid pressure fed through the conduit 22 and applied to the counter-balance valve [5.

Two ports 23 and 24 are provided in the main valve housing disposed opposite sides of a central land '25 of the spool, both of these ports communicating via a median enlargement 26 of .the bore :of the valve housing with a discharge :port .2?! communicating directly with the reservoir. "That is 'to .say the supply line 3 from the pump is, Within the valve housing, branched as at 31) into two passages communicating with the two ports 23 and 24 through which the oil under pressure flows through the valve housing 1 into the appropriate parts of the circuit. Two further lands 28 and 29 are provided on the valve spool =5 @equidistantly spaced [from the :said central .land 25,, the land 28 :serving .at the appro- .priate stage to :close-a port 30 in the valve housing and comprising one end'of a passage Bil in \the valve housing PI feedinga conduit .3la flared .outes at-3 lb .(see Figure 10) for-connection bya :conduit 3410 to one end of the :jack cylinder 13, and the other land 29 being greater in axial dimension and closing a port 32 .-for a passage 33 communicating with the other end of the jack cylinder via a piston type .check valve member .50 having-a spherical head-pressedlby a spring 51 against a seating ring 56 serving as a .port 55, 1a IlaredpassageAQ symmetrical withrespect to the .flared passage 31b and thence by a conduit 49a .to the jack cylinder, the passage .49 being extended inwardsasat 49bto a port 58 in the .main valve, the check valve 50 serving to close the port 55,, the bore 5.1a accommodating the spring 51 being open to the passage .49 behind the .spherical head of the valve .50. .As will .be apparent, the latter mentioned .end of the jack cylinder is that which receives the fluid pressure appropriate to ,raising the blade of the bulldozer or equivalent load, it being preferred to carry the .piston ,rod .14 of the jack through the other endof .the cylinder-so that the maximum volume .space obtaining in thejack cylinder is that which receives the fluid pressure when the bulldozer blade is fully raised.

End lands 153 and 54 are formed on the 'main valve Spool '5, and communication between the port .30 and the control valve I5 is effected via an end port 5'1 in the bore 6 and a passage '52 leading from 'thisport 5| to "the port 20 of control valve l5 and also to a port .5Ia at the other end of the'bore '6.

Inthehousing lparallel with and spacedifrom the bore :6 containing the main valve spool .5 is .a cylindrical bore 34 (see Figure '10), ports 38 and 39 communicating with this bore, the bore .containing a counter-balance control valve or shuttle valve member taking the form of two coaxial opposed hollow piston-like valve members 35 and 36 closed at their outer ends and accommodating a coiled compression spring 31 tending 'to urgethem apart, this coiled compression spring when extended to the prescribed limit maintaining the two cylindrical valve members 35 and 35 .apart to close the two fluid pressure "ports '38 and 139. Thus, the bore. and shuttle valve member therein canbe regarded as comprising the counter-balance control valve. It will be notedthat this latter mentioned valveis a shuttle valve and is referred to .as the counter-balance control valve as distinct from merely the counter-balance valve l5. A further port 33a is provided in the bore 34 to connect at the appropriate time the passage 33 with the port 39 and conduit 22. The ports 38 and 39 branch as at 4311 (see Figure 14) into a common passage 40 leading to the conduit 22, the end of which communicating with one end of the housing of the aforesaid counter-balance valve I5 is restricted as at 22, the other end of this conduit 22 communicating also by a restriction 22b with one side of a spring loaded piston element 4| of an overload valve 42, the housing of which (see Figures 9 and is secured at one end by lugs 42 to the main valve housing, and in this end of the housing 42 the conduit 3 between outl-et of pump and main valve bore 6 communicates with the other side of the piston element 4| which normally closes an escape port 4|a and by reason of it being exposed to direct pressure from the pump serving to relieve excessive load in the conduit 3 should this occur during the hold stage, this communication being indicated diagrammatically in Figures 1 to 7 at 3 as a branch taken off the conduit 3 from the pump serving the main valve. This overload valve contains a conical maximum pressure control valve member 43 adapted to be opened when the fluid pressure in the said conduit 22 reaches a predetermined maximum pressure, e. g. one

thousand pounds per square inch, a coiled compression spring 44 normally maintaining this maximum pressure control valve member seated against the reduced diameter end 45a of a bore 45 in an axial valve element 46 screwed into the valve housing 42, the bore 45 partly accommodating a spring 4|a loading the valve element 4|,

oil escaping through bores 45b when the relief valve member 43 is raised from its seating. The aforesaid restriction 22b fitted in the connection from conduit 22 allows the overload valve member 4| to open after the maximum pressure valve, to relieve the pump, in known manner.

A restricted passage 41 connects to a pair of vent ports 42 the junction of the two passages 38 and 39 of the counter-balance control valve containing the counter-balance control valve members 35 and 35 so that when the counter-balance control valve is in its normal condition, i. e. with its two slidable cylindrical members 35 and 36 held apart by the interposed spring 31, the said conduit is vented to the reservoir via restricted passage 41, median part of bore 34 and ports 48 to ensure that valve element 4| can act freely as a low pressure relief for the pump whilst by-passing, the vent being closed when valve elements 35 or 36 shuttle.

Any tendency for there to be a deficiency of oil in the complete circuit is taken care of by providing in the passage 52 which returns the oil from the jack to the reservoir via the counterbalance valve l5 a replenishing valve such as e. g. a ball valve 6!] which is normally maintained on its seating by the return pressure in the circuit but which will be raised to admit the appropriate amount of oil to replenish the circuit should there be a deficiency of oil in the circuit.

To explain the operation of the valve mechanism, reference will now be made to the diagrams of Figures 1 to '7. In the hold position of the main valve spool 5, as shown in Figure 1, the part I! of the counter-balance valve l5 by the action of the spring |8 is held in the position which cuts off the escape of oil to the reservoir via the port 200. so that the oil in the passage 52 of the main valve is blocked under substantially no pressure.

It will be seen that in this hold position of the main valve spool, the ports 23 and 24 are open to the enlargement 26 (see Figure 10) and the outlet 21, so that when the jack is held immovable the pump 2 freely circulates the oil back into the reservoir via the two ports 23 and 24, the flow of oil to the jack from the main valve being prevented by the two lands 28 and 29 on the main valve spool, the land 23 closing the port 30 communicating via passage 3| and conduit 3 I 0 leading to one end of the jack cylinder l3, and the other land 29 closing the port 32 for the passage 33 communicating with the other end of the jack cylinder via the check valve member 50. Consequently the oil in the jack cylinder at the side remote from the piston rod I4 will, under the influence of the Weight of the bulldozer blade, be blocked under pressure in the cylinder, conduits 49a, the passages 49 and 4% up to the closed port 58 in the main valve. The oil in the conduit 3|c and passage 30 between the jack piston l4 and land 28 of the main valve spool, and also the oil in the passage 52 between land 28 and the counter-balance valve l5 and replenishing valve 65 is blocked under no pressure.

In moving the main valve spool 5 in the direction to open the port 32, i. e. to the right from that shown in Figure 1 to reach the raise position shown in Figure 2, the port 32 is opened by the displacement of land 29 to establish communication with the end of the jack cylinder l3, i. e. the right hand end in the diagrams, which will drive the jack in the direction of the arrow shown in Figure 2 to raise the bulldozer blade (i. e. to the left looking at Figure 2).

Before communication is established the valve mechanism passes through the condition shown in Figure '7 where part of the pump delivery enters passage 33 to move counter-balance control elements 36 against the other element so as to close oil the restricted passage 4'! from the outlets 48 and open port 33 and via passage 43 and line 22, connect the pump pressure to the restricted inlet 22 of counter-balance valve l5 to overcome spring l8 thereof and open port by the displacement of valve member It, i. e. the head H of this valve member 6 uncovers the escape port 20 before the bypass passage 23 is closed. Pres sure from conduit 22 also reaches the chamber 42b in the overload relief valve 42 so that the pump pressure can be raised above idling. As the bypass passage 23 closes, oil under pressure from the pump flows through port 33a against the check valve 50 overcoming the load thereon from the suspended bulldozer blade and flowing to the jack cylinder via opened port 55, passage 43. and conduit 49a. Fluid displaced from the left hand end of the jack cylinder (looking at Figure 2) returns to the tank from the jack cylinder via the passage 3| and ports and 5| of the main valve housing and passage 52 by reason of the land 23 of the main valve spool 5 being moved away from the port 30 communicating with the appropriate end of the jack cylinder. It is important to note that the check valve member 50 is opened only when the pressure due to the operation of the pump is sufficient to raise the bulldozer blade. This check valve 5|! consequently forms a positive seal during the hold position of the main valve shown in Figure 1 to prevent the blocked oil in the passage 49 under the pressure of the bulldozer blade or equivalent load from operating against the said counterbalance control valve member or reaching the pump or bypass ports during movement of the main valve spool before the 7 :pump'has built up sufficientipressure to overcome the load, the ffinal blocking of this 'oil :being due :to-theclosure of ."the'port 158 in .the main :control valve housing by the outer end of the land129 of the main valve spool.

Byxmeans :of :the foregoing the pressure generated for lifting the bulldozer blade is only that required to actually lift the blade 'to the afully raised position, and :pressure above this stage will be relieved by the aforesaid maximum :pres- :sure control valvemember. with which the appropriate end of the aforesaid conduit L22 .communicates via restriction 22a, it being understood that during the raise stage the relief valve member M is subjected to balanced pressure from the :pump.

When lowering the bulldozer blade pressureis applied to the appropriate end of the cylinder 13, i. e. the left hand end looking at the diagrams, moving the spool to the positions'hown in Figure this movement being in the reverse direction to that in which it was'moved to effect a raising of the bulldozer "blade, i. e. by moving the crank 6 to the position marked lower in Figure 9, :and

this has the effect of shifting over the counterbalance control or shuttle valve members :35 :and '36 to the opposite position to that shown in Fig- "ure .2 so that these members .35 and 36 occupy the position shown in Figure '3, this resulting "from-the change in the end of exposure of such valve members to the pressure from the pump, the pump pressure now passing through the port 30, passage 3| and conduit-3 la to the appropriate end of the cylinder 13, the oil pressure in the passage 3| acting on the memberi35 of the .counter-balance control valve to effect the saidshifting over of this valve and thereby opening port 38 and admitting oil pressure to the conduit :22 via the passage 40, so that the counter-balance valve 15 is again moved to the position it occupied during the raise stage. Arising from this the discharge port 29a of the counter-balance valve will discharge the oil'from the right hand end of the jack cylinder 13 via the spring side of the said check va lve 50, and port 55 of the counter-balance control valve, passage 4%, port :58 and 5Ia of the main valve and passage 52. The oil between the check valve member '50 and the counter-balance control valve member 36 is :now trapped by reason of the larger axial dimension land 29 of the main valve spool closing the port 24 through which oil under pressure passes :from the main valve when the valve spool is set in "the position for raising the bulldozeriblade. It fis-important to note that 'under these conditions it is only possible to discharge oil from the right hand end of cylinder 13 whilst pressure is maintained in the left hand end of the cylindenthusensuring that the discharge from the cylinder is :proportional to the rate of feed'from the pump,'i. e.-.the rate of lowering the bulldozer blade is controlled by the pump thus maintaining the hydraulic system full of oil.

When the valve mechanism is to be set to the float" position i. e. when the bulldozer blade is to be free to float downwards or upwards, the main valve spool 5 is moved still further to the left to the floatposition (see Figure 4) beyond the position in which it was moved for lowering the bulldozer blade, and this has the effect of establishing communication-from the pump with the reservoir via passage 3, port 23 andthe outlets 26, 21 at the median part ofthe main valve housing. The pump is thus by-passed, so that the pressure in the :passage 3 to the outlet .21 is ?bypass pressure. This has the effect of any \oil :under light pressure in the circuit :passages .22 and -52 maintaining open the port 20a {Of :the counter-balance valve ii 5 by'whichthe oil returns to the reservoir, and also displacing under light pressure the counter-balance control or shuttle valve members :and 36 to the same ,position they occupy during lowering. The main valve "spool 5-also occupies the same position as shown .in Figure 4 when the bulldozer blade is floating in the upwarddirection -(see :Figure :5) the gpump still'circulatin'g idly under bypass pressure -.to .the tank or reservoir through outlet 121. This latter float condition can be that which obtains "when .the bulldozer blade is trailing .on the groundzand the bulldozer is being moved, and as with the float down condition shown in Figure A, both sides of the ,j ack cylinder communicate :with the counter-balance valve l5, but as there .45 new practically no pressure in thecircuit the .-s pring 3 1 reasserts itself to return the valve members 35 and'36 to thesameposition as that occurring during hold condition shown in :Figure l. There is :now no pressure in the conduit :22 acting upon the valvemember 21 of the counter-balance valve [5 consequently the port 20a of this latter valve is closed. The result is a closed cylinder'circuit and any displacement -.of the "j ack piston will .result in suction being'created in theclosedcircuit and the lifting of the replenishing valve 60 ,to maintain the closed circuitcompletely-charged.

On moving the main valve spool 5 towards the lowering position (see Figure 6)., on its way .to the :full lower position the spool 5 will bring l .theland partly over the port.30 which will admit the :oil under by-pass pressure to :the left hand :end'of the jack cylinder, andalso the land 25 will partly open the port 58 and thereby admit suspended-load pressure, i. e. the pressure due to the weight of the suspended bulldozer blade, as far as the counter-balance valve ,l 5 via the rear of check valve 50, port-58 and passage-52.

Assuming that the maximum pressure control valve-43 is adapted to .be opened at 1,000 lbs..per .sq. inch, the overload relief valve 41 can Jae adapted to be opened at about fifty ,five lbs. per sq. inch and the counter-balance control valve members :35 and 36 opened at twenty to forty-lbs. per :sq. inch, with the check valve .50 :opened at fifteen lbs. per sq. inch. With such anexample the counter-balance valve I5 will be operated at from forty-two to seventy-four lbs. 'per sq. inch, whilst the replenishing va1ve'60 can be operated 'at-0:5' lb. per sq. inch.

We claim:

1. Means for controlling the raising, ilowering, maintaining raised and floating conditions of a load to be controlled hydraulically, comprisin a jack for raising and lowering the load, armain valve of the .sliding spool type, manually controlled means to actuate said spool, a pumpgencrating hydraulic fluid pressure to actuate the j ack 'in :the load raising and lowering directions, an oil reservoir accommodating the pump -:and said valve, said valve controlling-a hydraulic circuit served by said pump and including connections to opposite ends of the'jack from the pump via said main valve, and *a connection to a return or discharge outlet to the reservoir from the ends of the jack via said valve, a counter-bala'nce valve controlling said return or discharge outlet and being actuated by load-operative fluid pressure during actuation of .the jack to .open said outlet and by means yieldably opposing saidpres- .sureto-close said outlet when the main valvespool is set to isolate the pump from the jack, a shuttle valve exposed to the said connections to opposite ends of the jack and which adapts itself positionally automatically in conformity with the selected one of said connections being served by the pump, connections from said shuttle valve to said counter-balance valve by which the pressure in the pump circuit can be applied to and isolated from the said counter-balance valve so that said counter-balance valve will not open the connection from the appropriate end of the jack cylinder to said discharge outlet until the said shuttle valve is actuated by pump pressure to introduce a control of said discharge opening which is dependent upon and maintained by the fluid pressure in the said connections to the jack so that the discharge from the jack cylinder must be proportional to the rate of pressure feed from the pump to the jack cylinder, and a check valve in the connection which serves the load raising side or end or" the jack and serving to isolate the shuttle valve from the oil under pressure between said latter side or end of the jack and the main valve when the main valve spool is set otherwise than in the position at which the load is being raised by the jack.

2. Means for controlling the raising, lowering, maintaining raised and floating condition of a load to be controlled hydraulically according to claim 1, wherein the said counter-balance valve is held normally in the closed position by spring means to retain oil in the appropriate part of the hydraulic circuit without pump pressure so as to block such part of the circuit, the influence of said spring means being overcome by pressure derived from the pump discharge during the operation of raising or lowering the load before discharge from the jack cylinder can take place, and the said shuttle valve is a counter-balance valve control located in the hydraulic circuit between the aforesaid counter-balance valve and a branch from the pressure line from the pump to the jack cylinder, said shuttle valve having opposed coaxial slidable valve elements controlling individually distinctive branch passages connecting the fluid pressure lines serving opposite ends of the jack cylinder distinctively to a common pressure passage to said counter-balance valve, the hydraulic pressure in said common pressure passage opening the discharge from the jack cylinder.

3. Means for controlling the raising, lowering, maintaining raised and floating conditions of a load to be controlled hydraulically according to claim 2, wherein said counter-balance control valve has one of its said slidable valve elements exposed for operation to the hydraulic fluid pressure in said connection leading to one end of the jack from the pump discharge and at a position between the said main valve and the said end of the jack, and has its other slidable valve element along with said check valve exposed to the hydraulic fluid pressure in said connection leading from the pump to the other end of the jack and at a position between the main valve and said latter end of the jack cylinder, said counterbalance control valve elements under the influence of jack operating pump pressure opening ports both communicating with a discharge port of said counter-balance valve, the main valve having a pair of end discharge ports communicating with said discharge port of said counterbalance valve and a further pair of ports both communicating with the pressure line from the pump, and a by-pass port between said latter pair of ports, the valve spool having a pair of axially spaced lands adapted to close simultaneously and to open selectively a further pair of ports serving the distinctive pump pressure line connections from the main valve to the ends of the jack and in the position closing both of said latter line connections and opening said by-pass port for idle oil circulation by the pump, a further port in the main valve opened and closed by one of said lands by which is maintained and released the blocking under the influence of the weight of the load on the oil in one end of the jack cylinder, said latter mentioned port communicating with said one end of the jack cylinder and the said latter land controlling the connection of the one end of the jack cylinder to one of the said end discharge ports, the other of said two lands controlling the connection of the other end of the jack cylinder to the other of said end discharge ports, a third land being formed on the main valve spool between the aforesaid lands to isolate the main valve port serving the latter end of the jack cylinder from the pump when the said by-pass port is exposed for said idle oil circulation by the pump.

4. Means for controlling the raising, lowering, maintaining raised and floating conditions of a load to be controlled hydraulically according to claim 2, wherein the connections from the said main control valve to the discharge port of said counter-balance valve also communicate with a replenishing valve.

5. Means for controlling the raising, lowering, maintaining raised and floating conditions of a load to be controlled hydraulically according to claim 3, wherein the connections from the said main control valve to the discharge port of said counter-balance valve also communicate with a replenishing valve. I

JOSHUA CHALLINER NAYLOR. J GEN NELSON FIELDI-IOUSE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,451,013 Ziskal et al. Oct. 12, 1948 2,477,669 Stephens Aug. 2, 1949 2,608,824 Kirkham Sept. 2, 1952 2,611,246 Ackerman Sept. 23, 1952 

